The present invention relates to an optical disk apparatus for recording digital image data, digital audio data, system data, and the like on optical disk media including magneto-optical disks and, more particularly, to an optical disk apparatus for recording data at a high density with an almost constant recording wavelength and for reproducing the data.
Conventional methods for recording data on an optical disk at a high density with a constant recording wavelength have included a constant angular velocity (CAV) scheme and a constant linear velocity (CLV) scheme. With respect to the constant angular velocity scheme, in performing a recording operation, the rotational speed of a disk is kept constant, whereas the recording bit rate is increased in proportion to the radius of each track. In the constant linear velocity scheme, when performing a recording operation, the recording bit rate is kept constant, whereas the rotational angular velocity of a disk is decreased in proportion to the radius of each track.
FIG. 34 shows an optical disk apparatus for recording data with an almost constant recording wavelength by the constant angular velocity scheme. This apparatus is disclosed in U.S. Ser. No. 08/334,272 filed by the present applicant. This invention is characterized in that data is recorded/reproduced on/from only one surface of an optical disk by using one head.
Referring to FIG. 34, an optical disk 1 is driven by a disk drive section 11 to rotate at a constant angular velocity. An optical head 2 is driven by a head drive section 3 to move in the radial direction from the inner periphery to the outer periphery of the optical disk 1, as indicated by the arrow in FIG. 34, write recording data Dw2 on the optical disk 1 or read data recorded on the optical disk 1, and output it as reproduction data Dr1. A track position detector 4 receives position information P1 from the optical head 2 and outputs a signal P2 indicating the position of a track.
A recording control signal generator 5 outputs a recording clock signal Cw1 on the basis of the track position signal P2 so as to increase the recording bit rate in proportion to the radius of each track. A recording data processor 6 performs video/audio synthesis, shuffling, addition of an error correction code, modulation, addition of a sync signal, and the like with respect to recording input data Dw1, and temporarily writes the resultant data in a recording buffer memory 7. At the same time, the recording data processor 6 reads data from the recording buffer memory 7 in response to the recording clock signal Cw1, and outputs the data, as the recording data Dw2, to the optical head 2.
A reproduction control signal generator 8 outputs a reproduction clock signal Cr1 on the basis of the track position signal P2. A reproduction data processor 9 temporarily writes the reproduction data Dr1 read by the optical head 2 in a reproduction buffer memory 10 in response to the reproduction clock signal Cr1. The reproduction data processor 9 also performs sync signal detection/demodulation, error correction, deshuffling, video/audio separation, and the like with respect to data read out from the reproduction buffer memory 10 at a predetermined rate. The reproduction data processor 9 then outputs the resultant data as reproduction output data Dr2.
Assume that data to be recorded is intraframe-coded data having a frame frequency of 29.97 Hz (30/1.001 Hz). In this case, the rotational speed of the optical disk 1 is set to be 29.97 rps, which is synchronized with the frame frequency, and the optical head 2 is moved from the innermost track to the outermost track, thereby recording the data. Note that the rotational speed of the optical disk 1 may be synchronized with the field frequency.
In addition, the track area of the optical disk 1 is divided into equal areas in the radial direction, and data is recorded on each divided area at the same bit rate. For sake of descriptive convenience, assume that the radius ratio between the innermost periphery and the outermost periphery of the track area is 1:2, the track area is divided into nine equal areas in the radial direction, and the amount of data per frame is eight sync blocks. A sync block (abbreviated as SB) is a fixed-length data string consisting of a sync signal, an ID signal indicating an address, image data, an error correction code, and the like. In practice, the number of sync blocks per frame is about 800.
Each of the nine equal track areas is called a clock block (abbreviated as CB). Let CB0 be the innermost clock block, and CB8 be the outermost clock block. In this case, if the number of tracks per clock block (CB) is eight, the optical disk has a track format like the one shown in FIG. 33. Note that the numbers written on the left ends of the frames of clock blocks CB0 to CB8 are track numbers; the numbers written in the frames, the frame numbers of recording data; and the numbers within the parentheses, the numbers of SBs.
In CB0 on the innermost periphery, a total of 8-frame data are recorded, providing that 1-frame (8 SBs) data is recorded per track. In CB1, a total of 9-frame data are recorded, providing that 9-SB data are recorded per track. In CB2, a total of 10-frame data are recorded, providing that 10-SB data are recorded per track. Subsequently, the amount of data to be recorded per track is increased by 1 SB for each clock block (CB). In CB8 on the outermost periphery, a total of 16-frame data are recorded, providing that 2-frame (16 SBs) data are recorded per track. In this manner, a total of 108 frames, from frame #0 (the symbol "#" represents "number") to frame #107, are recorded within the range of track #0 to track #71 on the optical disk.
In order to record data on tracks at a bit rate corresponding to each divided track area, i.e., each clock block (CB), data written in the recording buffer memory 7 at the frame period is read out at a period shorter than the frame period. For this reason, a data shortage occurs in the recording buffer memory 7. Therefore, timing adjustment (called pause track processing) is executed to stop recording data on a track when a data shortage occurs. More specifically, the recording control signal generator 5 outputs a pause track control signal Cw2 to the recording data processor 6 on the basis of the track position signal P2. In this case, since data shortages occur in the recording buffer memory 7 at specific track positions, the track positions where pause track processing is to be executed are stored in a storage device such as a ROM in advance.
In the reproduction mode, data reproduced from tracks is written in the reproduction buffer memory 10 at a period shorter than the frame period and is read out at the frame period. Consequently, an overflow of data occurs. For this reason, when an overflow occurs, the optical head is moved backward by one track to read data from the same track twice (this processing is called repeat track processing). More specifically, the reproduction control signal generator 8 generates a repeat track control signal Cr2 on the basis of the track position signal P2. In this case, since overflows occur in the reproduction buffer memory 10 at specific track positions, these track positions are stored in ROM or the like in advance.
In the above optical disk apparatus is designed on the basis of a normal state in which the rotational speed of the optical disk 1 is synchronized with the frame period. For this reason, the apparatus uses a ROM or the like in which track positions where timing adjustment is executed are stored in advance, and executes pause track processing and repeat track processing in accordance with the track positions. If, therefore, the rotational angular velocity of the optical disk 1 exceeds a predetermined frame period owing to a servo shift or the like, a data shortage occurs in the recording buffer memory 7, or an overflow occurs in the reproduction buffer memory 10. As a result, a normal recording/reproducing operation cannot be performed.
Assume that 1-frame data is recorded on a track per revolution. In this case, when the optical disk 1 normally rotates at 29.97 rps in reproducing data from this track, data is reproduced at a rate of 29.97 frames per second, and hence no problem is posed. If, however, the rotational speed of the optical disk 1 exceeds the normal rotational speed and becomes, e.g., 31 rps, the amount of data to be reproduced increases to 31 frames per second. Even if, therefore, a certain increase in data amount can be absorbed by the reproduction buffer memory 10, an overflow occurs in the reproduction buffer memory 10 to finally cause a data error.
Furthermore, in this optical disk apparatus, the positions where pause track processing is executed are determined according to one pattern. For this reason, it is difficult to execute pause track processing at the optimal positions corresponding to changes in the capacity of a buffer memory for absorbing jitter.
Since the size of the innermost periphery of an optical disk must be matched with the minimum recording unit, it is difficult to realize high-efficiency use of the disk and high-capacity recording by using the innermost periphery.
In addition, the above apparatus is designed in consideration of only recording of a 525/60 component television signal in the NTSC zone, but no consideration is given to the common use of the apparatus for recording of a 625/50 component television signal in the PAL zone.
Moreover, no consideration is given to shuffling to be performed in recording compressed data by MCAV.